High-power electronic tube, in particular a microwave tube with improved cooling

ABSTRACT

In order to make it possible, using air in particular, to cool certain high power tubes the collector of which has dimensions too small to permit of such cooling itself, the invention provides for the association with the collector, cooled by evaporation of liquid, of a large-area element delimiting a closed volume partially occupied by the liquid mass in question, the cooling of said element being responsible for producing condensation of the vapour resulting from said evaporation, and the regeneration of the liquid mass.

United States Patent 1191 Ninerailles et al.

Jan. 7, 1975 HIGH-POWER ELECTRONIC TUBE, IN PARTICULAR A MICROWAVE TUBE WITH IMPROVED COOLING Inventors: Jacques Ninerailles; Auguste Raye,

both of Paris, France Assignee: Thomson-CSF, Paris, France Filed: May 11, 1973 Appl. No.: 359,216

Foreign Application Priority Data May I6, 1972 France 72.l7440 us. 01. 313/34, 313/46 1111. C1. 11011 23/04 Field of Search 313/34, 46; 315/538 References Cited UNITED STATES PATENTS 5/1969 Hansen et al. 313/34 Primary ExaminerJohn Kominski Assistant Examiner-Darwin R. Hostetter Attorney, Agent, or Firm-Roland Plottel [57] ABSTRACT In order to make it possible, using air in particular, to cool certain high power tubes the collector of which has dimensions too small to permit of such cooling itself, the invention provides for the association with the collector, cooled by evaporation of liquid, of a largearea element delimiting a closed volume partially occupied by the liquid mass in question, the cooling of said element being responsible for producing condensation of the vapour resulting from said evaporation, and the regeneration of the liquid mass.

4 Claims, 6 Drawing Figures PATENTED JAN 7 I 75 SHEET 10F 3 PATENTED JAN 7 5 SHEET 30F 3 HIGH-POWER ELECTRONIC T-UBE,;IN PARTICULAR A MICROWAVE TUBE WITH .IMPROVED COOLING The present invention relates to an. air-cooled electronic tube. A y The, electron beam utilised in an electronic tube is available for dissipation, whereas, considered in this picked up, after passingthrough the tube, in'a collector. The latter must be capable of dissipating the power carried by the bearn'iatlthe instant of its impact upon the collector. This power is a variable fraction ofv the power applied'to the tube, the fractiondepending upon the tube efficiency. It generally increases with the I power applied to the tube so that the higher said power is themore effective mustbe the cooling of the collector, other things being equal. I 5 i The collector itself, has dimensions, in particular a" dissipative area, which are limited by various considerations which in effect mean that these dimensions cannot be increased in' propo rtion' with the power dissipated. Thus, for'example, in microwave tubes, where the electron beam frequently takes the form of a cylindrical beam of smallsectio ngthe fanning out of the beam in the collector must be restricted in order to prevent heating up of certain parts of the tube, an effect which could interfere withproper operation of the latter. I I

same context, a power of at least one kilowatt would have to be reached, when operating in the decimetre waveband, before starting to talk about high power.

An example willbe used to make this point clear, in the ensuing text.

.To make it possible to cool the tube, the invention provides for the association with the tube collector of a large-area element exposed to a cooling fluid, the dimensions of which element can be chosen independently of the criteria, listed hereinbefore, which the collectoritselfhasto satisfy. This element is firmly coupled with the collector, the connection being provided by a'body of liquid bathing the whole of the collector and raised to boiling point by the thermal energy result- 'of FIG. 1;

Consequently, it is generally necessary to arrange for levels of heat dissipation 'per unit area of the collector, I

which are progressively higher and higher, the higher the power applied tothe tube.

These unit dissipation levels'far surpassthose which can be achieved by naturalcooli'ng through dissipation I to the environnement. TlllSlS why recourse is'had to an auxiliary fluid which is maintainedin-contact with the collector under conditions'which make is p ossible to substantially exceed the cooling levels which arepossible when using natural cooling.ji

We shall not concern ourselves here the numerous solutions whichihave been introduced, for the solu- FIG. 3 is' a diagram relating tothe devices in accordance with the invention;

FIGS. 4 and 5' are perspective views of two other embodiments of the tube in accordance with the invention. 1

FIG. 6 is a' variant embodiment of FIG. 1. FIG. 1 illustrates an electronic tube in accordance .with the invention. In this figure, the reference 1 signifies the base of the tube, that is to say that part thereof,

" through which the connections or leads (they carry no references) of the various tube electrodes, pass, the reff erence 2 signifies the tube bod'y and the reference 3 the tion of this problem, within the enormous fieldofelectronic tube design, although the essential character of these solutions should be firmlyborn'e inim'ind, ecause more often than not it is the possibilities affordedfor cooling which finally fix the peak'po.wers "of the tubes which can beproduced. We should not omit, either, to point out that these solutions sometimesutilise a gas, generally air, andsometimes a liquid, ,depem'dingupon the powers to be dissipated per area, liquidsnaturally being reserved for the highest powers, 1

" However, for reasons external of thetube itself, environmental' reasons,.in particular accessibility, it some comes up against difficulties. I v U The object of the present invention is tto overcome these difficulties. The invention relatestoanelectronic times happens that the application of these solutions A i tube of high power, incorporating improved cooling. 3

Self-evidently, the concept of high power do es'not commence from a determinate power'le vel, but depends upon the assembly of the other characteristics of the tube; in the microwave range in particulahwhere mensions thoseof the collector, this conceptis closely associated with the wavelength. Thus, the tube putting out just a few watts, in the millimetre waveband, is-a hight power tube considered vis-a-vis the facilities electron collector whichhas ashape suitable. for performance of cooling by the evaporation of liquid. Collectors of this k-indhavebeen described in numerous Patents of the present'Applicants, in particular U.S. Pat. No. 3,299,949,'to which referen'cemay usefully be made. 'In this figure, 4 designates. the mass of cooling liquid which is raisedito theboiling point'when the tube is operated. There can also be seen in this figure an elongated part 5 which enshrouds the collector 3 and contains the mass of liquid in question. This part takes the form of a cylinder closed at itstopend, the mass of liquid ,4 occupying the 'bottom end. This cylinder, which is narrowed at its bottomend to a diameter close to'thatof thecollector, is equipped with fins 6, cooled bya'gazeous fluid, generally air.

It will beseen from this figure that the liquid occupies- Only a'small part of the height of the cylinder 5, the whole of the remainder of the. height being empty of any liquid,.-fln operation, the liquid mass is raised to the boiling point by the 'heat picked up by the collector under the effect of bombardment with the electrons of th'e beam propagating through the inside of the electhe operating wavelength almost invariablyfixes the general dimensions of the tube, and amongst these ditronic tube. The vapour produced by boiling fills the freespace inside the cylinder 5 and is condensed by contactwith' the walls thereof due to the cooling which it experiences. The cooling in question, as in the example of the figure, is produced by the forced circulation of air over the fins 6 This circulation is symbolicallyindicated by the arrow. 1

The cylinder 5 behaves as an isothermal enclosure for the vapour or as a heat-transfer cylinder which ineludes the heat source, the collector in this case. The condensedvapour drops back to the bottom of the cylinder under gravity, the assembly being vertically arranged for the purpose.

In the example shown in the FIG. 1, a second cylinder 7 concentric with that referenced directs the condensed vapour towards the mass of boiling liquid. This cylinder, illustrated in the example of the figure as a continuous metal surface, could equally well take the form of a mesh or grid; such a grid is shown in FIG. 6 in which it can be seen a part of FIG. 1, i.e. part of the cylinder 5, equipped with the fins 6, the mass of liquid 4 occupying the bottom end of the cylinder 5 and the grid 70, cylindrically shaped. The grid 70 (FIG. 6) or the cylinder 7 consisting of a continuous metal surface (FIG. 1) constitutes a kind of wick the structure of which, within the context of the present invention, can take a variety of forms in order to produce this directing function. Screws 8 enable the wick 7 to be maintained in position in relation to the cylinder 5.

A device of this kind has been produced in a slightly different form from that utilised above, for a tube operating in the Ku band (16 gigacycles). The tube in question produced an output power arranging between 1 and 2 kilowatts at this frequency, for an input power of some 20 kilowatts. The approximate calculation made in respect of this tube, is given herebelow.

The collector took the form of a hollow metal body, the cavity in fact taking the form of a cylinder about 8 cm high and 12 mm in diameter, whilst the external dimensions of the collector were those of a cylinder having a diameter of 60 mm and a height of 9 cm. This collector was externally machined under the usual conditions specified in the Patentsreferred to hereinbefore, in order to enable evaporation cooling to take place under the vapotron system disclosed in these Patents. This kind of machining is not illustrated in detail, since it is a prior art, in the figures illustrating this kind of collector. Dimensions of this kind made it possible to achieve a dissipation of approximately 50 watts per cm using the kind of machining in question, that is to say a total dissipation equal to the 20 kilowatts of power dissipated in accordance with the above figures.

In the diagram of FIG. 3, the electron beam can be seen, the area covered with dots, reaching the collector at the end of its trajectory. As can be seen, this beam, assumed to be cylindrical, flares in the collector to a diameter D substantially greater than the diameter d which it has prior to reaching the collector. As can be seen, however, the space available for the beam, within the collector, is restricted, and consequently the coolingarea also limited. This is why, even with the aforementioned machining, which ensures an increase in the surface area of the collector, the effective collector area for heat dissipation is still limited, and consequently, the total possible dissipation which can be achievedlikewise.

In the same example, the component 5 was constituted by a hollow copper cylinder 1 mm thick approximately, narrowed at its bottom end and welded at said end to the body of the tube at the baseof the collector; the diameter and height of the non-narrowed portion, were respectively and cm. This cylinder was provided externally with 300 vertical fins 30 cm long, 3 cm wide and 1 mm thick. The cooling airflow was 1,500 m per hour, corresponding to a velocity of 25 m/s. The drawingof FIG. 1 actually illustrates another equivalent embodiment of the invention, with horizontal fins of which, for reasons of clarity, only a small number have been shown, their spacing not being to scale either.

The variant embodiment shown in FIG. 2 schematically illustrates a shape, on the part of the component 5, which differs slightly from that shown in FIG. 1 and is chosen in order to still further increase the cooling area offered by the component 5. In this figure, in the same way, the arrows illustrate the direction of the forced airflow over the fins. The reference 9 designates communicating passages.

It is possible in certain variant embodiments to utilise a liquid'mass, for example of water, which is very much in excess of that strictly required to bathe the collector of the tube. In this case, as the example of FIG. 2 shows, this water mass can occupy the major part of the internal volume of the cylinder 5, in contrast to what was provided in the case shown in FIG. 1 where it only occupied a small part of the volume. This arrangement has the advantage of giving the mechanism of condensation of the vapour in the body of that part of the mass of water located above the collector, an excellent thermal efficiency, without disturbing the dissipation of heat to the exterior, the metal-liquid heat transfer coefficient, although poorer than the metal-vapour heat transfer coefficient, nevertheless still being highly satisfactory.

Ultimately, it is questions of weight which determine the choice of one or the other of these embodiments. In the example illustrated, where the water mass was just sufficient to bathe the collector, the total liquid weight was 300 grams.

Generally, the cylinder 5 is evacuated before the tube is put into operation. In this case, the vacuum pip, not shown, through which evacuation has been carried out, is used as a safety valve.

FIG. 4 illustrates another embodiment of the tube in accordance with the invention.

In the example shown in this figure, the element 5 takes the form ofa highly flared funnel. As in the foregoing examples the bottom part of the funnel surrounds the collector 3 of the tube and contains the liquid mass 4 which bathes the collector. At the opposite end, the funnel is closed off by a plate 51 welded to its cylindrical portion 52. Welded to the plate 51 and to the flared part 53 of the funnel, there can be seen hollow cylinders equipped with vertical fins 61. The vapour coming from the liquid mass 4 flows over the external surfaces of the cylinders 60 whilst the cooling air is injected in the direction of the arrows, between the fins 61. The embodiment shown in FIG. 4 corresponds substantially to the numerical data quoted earlier; in this example, the cylinders numbered six, only three of which have been shown here; the external diameter of the cylinder portion 52 of the funnel was 42 centimetres and its height 15 centimetres, whilst the bottom cylindrical portion 50 had a diameter of 10 cm, the total height of the funnel being around 40 cm. Each of the cylinders 60, of stainless steel, had a thickness of approximately 1 mm, equal to that of the portion 50, 52 and 53 constituted in the funnel and of the plate 51, likewise of stainless steel; each cylinder 60 had an internal diameter of 12 cm, and had fins 1 mm thick and 4 cm wide. For the same reasons of clarity, these fins have not been illustrated to scale and their number has been reduced to just a few units, in the drawing of FIG. 4.

These fins, of aluminium, were integral with a central core 62; they were produced either by casting or by machining from a block and welded over their full height, using a known technique with an appropriate flux, to the cylinder 60 which itself is subsequently welded, by the argon-arc process, at both its ends and over the whole circumference, to the plate 51 on the one hand and to the flared portion 53 of the funnel on the other. The welding of the fins 61 to the cylinder 60 is visible at 71 in the figure, whilst the welds referred to earlier are respectively and partially illustrated by 70 and 72.

The FIG. 5 illustrates another embodiment of the tube in accordance with the invention.

In this example, the component 5 has the same form, namely that of a cylinder narrowed at its bottom end, as in the example of FIG. 1. In this figure, similar reference designate similar elements to those so marked in FIG. 1; there can also be seen a component 70 made of a material having good thermal conductivity, which enshrouds the cylinder 5 and is held in heat transfering contact therewith by an intermediate component 71. This component can for example be a layer of weld (solder) which ensures that the components 70 and 71 are in contact with each other over the whole of their mutually opposite surfaces. Also to be seen in this figure, is a solid component 72 of large dimensions which, because of the magnitude of these dimensions, could not be illustrated in full at the scale of the drawing, but which is in contact with the component 70 over part of the latters area.

In the example shown in the figure, the component 72 is fitted and welded at 73 (thick line) to the top end of the component 70. The dissipation of the heat is effected by conduction with the component 72 which is held in contact with the cooling fluid either directly or through the medium of a large-area element which is itself in contact with the fluid. The exemple shown in FIG. 5 relates to the first of these two possibilities. In this figure, the cooling fluid has not been shown. The fluid may, depending upon circumstances, be either a liquid or a gas.

Of course, the invention is not limited to the embodiment described and shown which was given solely by way of example.

What is claimed is:

1. An electronic tube comprising a collector, an electron beam producing an impact on said collector, and a mass of liquid in contact with said collector and raised to the boiling point by the thermal energy resulting from said impact, said electronic tube occupying a vertical position with the collector at the top, said mass of liquid occupying partially the interior volume of a closed envelope comprising a hollow cylinder closed at the top end of said tube, the liquid mass within which occupies the internal volume at the other end, over a fraction of the height, the interior surface of said envelope being made by at least a fraction of the exterior surface of the collector, the fraction of said volume not occupied by the liquid containing only the vapour of said liquid, said envelope being exposed to a cooling fluid, a wick being arranged inside said volume, which channels towards said liquid mass, the vapour condensed in that fraction of said volume not occupied by the liquid.

2. An electronic tube as claimed in claim 1, wherein said wick consists of a metal mesh arranged along at least a part of the internal wall of said volume.

3. An electronic tube as claimed in claim 1, wherein said cooling fluid is air in forced circulation.

4. An electronic assembly comprising: an electronic tube having a collector and means to produce an electron beam to impact on said collector; a closed envelope comprising a hollow member supported on said electronic tube, said collector extending into the bottom end of said hollow member, said electronic tube and said envelope occupying a vertical position; a mass of liquid within said envelope and in contact with said collector, said mass ofliquid occupying partially the interior volume of said closed envelope at the end of said envelope opposite the closed top end; the portion of said volume not occupied by the liquid containing only the vapor of said liquid; and wick means disposed within said envelope to channel the condensed vapor toward said liquid mass at the bottom of said envelope. l= 

1. An electronic tube comprising a collector, an electron beam producing an impact on said collector, and a mass of liquid in contact with said collector and raised to the boiling point by the thermal energy resulting from said impact, said electronic tube occupying a vertical position with the collector at the top, said mass of liquid occupying partially the interior volume of a closed envelope comprising a hollow cylinder closed at the top end of said tube, the liquid mass within which occupies the internal volume at the other end, over a fraction of the height, the interior surface of said envelope being made by at least a fraction of the exterior surface of the collector, the fraction of said volume not occupied by the liquid containing only the vapour of said liquid, said envelope being exposed to a cooling fluid, a wick being arranged inside said volume, which channels towards said liquid mass, the vapour condensed in that fraction of said volume not occupied by the liquid.
 2. An electronic tube as claimed in claim 1, wherein said wick consists of a metal mesh arranged along at least a part of the internal wall of said volume.
 3. An electronic tube as claimed in claim 1, wherein said cooling fluid is air in forced circulation.
 4. An electronic assembly comprising: an electronic tube having a collector and means to produce an electron beam to impact on said collector; a closed envelope comprising a hollow member supported on said electronic tube, said collector extending into the bottom end of said hollow member, said electronic tube and said envelope occupying a vertical position; a mass of liquid within said envelope and in contact with said collector, said mass of liquid occupying partially the interior volume of said closed envelope at the end of said envelope opposite the closed top end; the portion of said volume not occupied by the liquid containing only the vapor of said liquid; and wick means disposed within said envelope to channel the condensed vapor toward said liquid mass at the bottom of said envelope. 